Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/403—Cells and electrode assemblies
  • G01N27/406—Cells and probes with solid electrolytes
  • G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/403—Cells and electrode assemblies
  • G01N27/406—Cells and probes with solid electrolytes
  • G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
  • G01N27/4078—Means for sealing the sensor element in a housing

Definitions

• the invention relates to a sensor for measuring gas concentrations in a gas mixture with a tube closed on one side, on the outside of which an electrical sensor contact is arranged along the tube and whose end opposite the closed end is arranged in a housing, one running around the tube Intermediate space between the housing and the tube is closed in a gas-tight manner.
• Such a gas sensor is known from US-A-3960693.
• a tube with a catalytically active layer is closed at its end facing the gas to be measured and open at its other end. It is thickened at this open end and held in a housing.
• This housing is screwed into a wall opening of the room with the gas to be measured, for example in internal combustion engines.
• the inside of the tube is connected to the ambient atmosphere, the reference gas.
• a gap between the housing and the tube is sealed within the housing, so that the two different gases are separated from one another.
• the seal is made of a metal ring, as is commonly used for example in spark plugs. Gas measurements of this type are usually carried out at high temperatures (from around 150 ° C, in internal combustion engines from around 500 ° C).
• the housing which is made of metal because of the required temperature resistance, is thus conductively connected to the tube, that is to say the sensor contact.
• the housing is integrated in the measuring circuit; the sensor is a so-called mono sensor. Since the seal is located in a region of the sensor arrangement which is heated very strongly during the measurement of a fuel gas, the different expansion coefficients of the housing and tube can lead to leaks and thus to measurement inaccuracies, since the seal has the different Can not compensate for expansion with certainty.
• the electrical contacting of the sensor contact is also located in this hot zone and can therefore only be implemented with a high degree of security and with considerable effort, since the contact materials tend to oxidize at the high operating temperatures.
• the hot contact of the seal with the tube which can usually be formed from a solid electrolyte, causes a parasitic voltage, the size of which varies greatly over time, because the slow oxidation or reduction of the seal is uncontrollable. As a result, the drift of the sensor characteristics is considerably deteriorated.
• a similar sensor is also known from EP-AO 520 528.
• EP-A-0 398 579 Another type of gas sensor is known from EP-A-0 398 579.
• a flat sensor element is arranged within a cylindrical metal housing, ceramic powder for fixing and sealing being arranged between the sensor and the housing. Due to the different geometries between the sensor element and the housing and due to the different expansion coefficients of the materials, leaks can also occur when heated. Sealing to the gas space to be measured is particularly problematic. Apart from this, the sensor element can easily be damaged by vibrations occurring during operation.
• the invention is based on the object of specifying a sensor of the generic type which ensures a reliable seal between the gas to be measured and the reference gas to be measured even at high operating temperatures and in which at the same time several sensor contacts, which are electrically insulated from the housing, can be implemented and in which no parasitic voltages arise which impair the drift characteristics of the sensor.
• the object for a sensor according to the preamble of claim 1 is achieved in that a gas-tight seal running around between the housing and the tube at the end opposite the closed end, which forms a cold end (or a cold region) of the tube, it is arranged that at least one electrical sensor contact is arranged in an electrically insulated manner from the housing on the outside of the tube and that the at least one sensor contact at the closed end opposite end of the tube opens and is connected to an electrical line.
• the cold end or the cold area of the tube is the area which is arranged outside the room with the gas to be measured and which is far enough from the room with the gas to be measured so that it heats up at most only slightly so that the seal to be preferably used made of an electrically insulating, elastic material is not destroyed and retains its elasticity.
• the specific necessary distance can be easily determined by a few tests or measurements.
• the contacting of the sensor contacts with further electrical lines also takes place; Here, high-temperature oxidation phenomena on the contacts are avoided.
• Different coefficients of expansion of the materials used play practically no role here, in particular with elastic seals, there are practically no thermal stresses, so that a high sealing effect can be achieved.
• a plurality of sensor contacts are arranged on the outer surface of the tube, it being possible for one or more sensor contacts to be designed as a heating contact. This avoids the use of a separate radiator which is pushed into the tube in known arrangements. This increases the heater's efficiency and reaction speed.
• At least one electrical contact can expediently be arranged on the inside of the tube.
• the tube is cylindrical and is therefore very easy to manufacture.
• it can be advantageous to apply an electrically insulating layer on the tube between the housing and the sensor contacts.
• at least a part of the outer surface of the tube has a solid electrolyte material that is electrical with at least one sensor contact connected is. It is also possible to form the entire tube from a solid electrolyte material.
• at least part of the outer surface of the tube to have a material whose electrical resistance depends on the gas concentration. In order to effectively cool the cold area, it is expedient that cooling fins are arranged on the outside of the housing.
• Figure 1 shows the tube of the sensor with sensor contacts
• Figure 2 shows a cross section through the sensor
• FIG. 3 shows the schematic representation of the sensor
• Figure 4 shows a further cross section through the sensor
• Figure 5 shows the structure of some assembly elements.
• Figure 1 shows the tube 1 of the sensor.
• the tube 1 is cylindrical and closed at one end. It is made from an electrically insulating material, for example aluminum oxide, or from a solid electrolyte material, for example zirconium dioxide. It can also be made of another material that has electrical insulation on its outside.
• Gas sensors 2 are arranged on the outside of the tube 1 as active elements. Furthermore, an electric heater 3 is placed on the tube 1. On these electrical sensor contacts, namely the gas sensors 2 and the heater 3, a thin, electrically insulating layer 4 is attached, which is, however, gas-permeable and which prevents the gas sensors 2 from becoming dirty. B. prevent exhaust gas components.
• the electrical sensor contacts 2; 3 arranged along the tube 1 open into so-called external electrodes 5 on the open side of the tube 1, to which the tube 1 is electrically contacted.
• a contact ring 6 is arranged on the end face of the open end of the tube 1 and serves to contact an electrical contact 7 arranged on the inside of the tube 1.
• This electrical contact 7 is necessary if the gas sensor 2 is an electrochemical sensor with reference gas.
• the reference gas is located inside the tube 1 and is, for example, equal to the ambient air.
• the tube 1 is arranged in the housing 8 shown in Figure 2.
• the housing 8 has at its tip, in which the closed end of the tube 1 is located, gas openings 9 through which the gas to be measured reaches the gas sensors 2.
• the housing 8 In the area of the closed end of the tube 1, the housing 8 has a nut 10 with an external thread 11, with the aid of which the sensor is screwed into the wall of the room with the gas to be measured. In the area of internal combustion engines, this space can, for example, be part of the exhaust system (for example, of cars). A seal 12 can also be arranged on the nut 10.
• the closed end of the tube 1 abuts the corresponding end of the housing 8 and is pressed against this end by a spring 13.
• the tube 1 is arranged at a distance from the wall of the housing 8 so that the electrical sensor contacts (gas sensors 2 and heater 3) have no electrical contact with the housing 8.
• An O-ring 14 made of an elastic and heat-resistant plastic, for example made of Teflon or Viton, is provided as the gas seal.
• This O-ring 14 serves as a seal of the gas space of the gas to be measured against the atmosphere surrounding the housing 8, so that, for example, the ambient air remains separated from the exhaust gases of an engine.
• the O-ring 14 also realizes a stable position of the tube 1 within the housing 8 and ensures the electrical insulation of the tube 1 or the sensor contacts 2, 3 from the housing 8.
• the O-ring 14 prevents the transmission of vibrations from the housing 8 onto the tube 1 and it compensates for different coefficients of expansion between the tube 1 and the housing 8, so that no thermal stresses can occur even with slight heating.
• Another O-ring 15 serves to contact the outer electrodes 5 with the connecting wires 16.
• the O-ring 15 is also made of an elastic, heat-resistant plastic. By means of this O-ring 15, the connecting wires 16 are reliably pressed against the outer electrodes 5, so that a reliable contact is guaranteed. It is also possible for the connecting wires 16 to be welded to the outer electrodes 5 or for the outer electrodes 5 to be contacted by a plug which is pushed onto the tube 1 and provided with connecting wires 16.
• the O-ring 15 is pressed against the O-ring 14 by the pressure piece 17, so that the tube 1 is held securely within the housing 8 by the additional tension generated thereby.
• the contact piece 17 is pressed against the O-rings 14, 15 by means of the nut 18 via the washer 19 (made of a heat-resistant plastic), the O-ring 14 being pressed against a stop surface of the housing 8.
• the mother 18 serves to close the Inner part of the housing 8; the connecting wires 16 and the connecting wire 20 are passed through them.
• the connecting wires 16, 20 are centered by the disk 19 and passed through the pressure piece 17 into the interior of the housing.
• the connecting wire 20 After assembly, the connecting wire 20 has an electrical contact with the spring 13, which in turn rests on the contact ring 6 in an electrically conductive manner, so that the connecting wire 20 contacts the electrical contact 7 in the interior of the tube 1.
• the arrangement of pressure piece 17, nut 18 and washer 20 is enlarged in Figure 5 and shown in several views.
• plastic seals as O-rings 14, 15 with the resulting advantages described above is possible in a region of the housing 8 which does not heat up significantly even at the operating temperature of the sensor, that is to say is only heated to such an extent that the plastic seals do not lose their elasticity.
• this area is at least approximately 2 cm, in particular approximately 4 to 6 cm, from the seal 12, which closes the space of the gas to be measured.
• the O-rings 14; 15 are usually arranged in an area in which the temperature is only so high that the materials of the O-rings 14; 15 can be used permanently.
• 8 cooling fins 21 are arranged on the outside of the housing.
• the distance between the rings 14, 15 and the closed end of the tube 1 can be reduced under certain circumstances.
• the number and shape of the cooling fins 21 as well as the length of the housing 8 can be selected as a function of the operating temperature of the gas to be measured, in order to ensure that the so-called cold end of the tube 1, on which the O-rings 14, 15 are arranged, warmed up only slightly so that the O-rings 14, 15 are not damaged and lose their function.
• FIGS. 3 and 4 show a longitudinal section through the sensor that differs somewhat from FIG. 2.
• the sensor according to the invention has a very simple and therefore inexpensive structure; With the possibility of accommodating several sensors in one and the same housing, it is not very susceptible to faults and is therefore safe to use.

Landscapes

• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Molecular Biology (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Measuring Oxygen Concentration In Cells (AREA)

Applications Claiming Priority (5)

Publications (1)

Family

ID=26016868

Family Applications (1)

Country Status (8)

Families Citing this family (4)

Family Cites Families (6)

• 1996
  • 1996-06-28 JP JP9506218A patent/JPH10506473A/ja not_active Withdrawn
  • 1996-06-28 EP EP96922042A patent/EP0781410A1/de not_active Withdrawn
  • 1996-06-28 TR TR97/00198T patent/TR199700198T1/xx unknown
  • 1996-06-28 CA CA 2200203 patent/CA2200203A1/en not_active Abandoned
  • 1996-06-28 CN CN 96190747 patent/CN1158164A/zh active Pending
  • 1996-06-28 BR BR9606523A patent/BR9606523A/pt unknown
  • 1996-06-28 AU AU63059/96A patent/AU708240B2/en not_active Ceased
  • 1996-06-28 WO PCT/EP1996/002835 patent/WO1997004306A1/de not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events